Question

A group of students wish to determine the launch speed of a specific 'launcher' device that they are using in a projectile experiment. The group is using the launcher to launch a ball horizontally from the top of their lab table, to land on the floor below. The group has already measured the height of the table, relative to the floor below.
Which one of the following sets of additional measurements would be adequate to allow the group to determine the ball's launch speed, without taking any extraneous/unnecessary measurements?

• A. Only the horizontal distance moved by the ball during its motion
• B. The horizontal distance moved by the ball during its motion, as well as the time required for ball to fall
• C. The time the ball falls for, as well as the mass of the ball
• D. The horizontal distance moved by the ball during its motion, the time the ball falls for and also the mass of the ball

Answer 1

The correct option is A Only the horizontal distance moved by the ball during its motion

Since only gravitational force acts on the projectile in the downward direction, the horizontal speed of it remains the same.
Considering motion in vertical direction,

$h=\frac{1}{2}g{t}^2$

$⟹t=\sqrt{\frac{2h}{g}}$(known)
Also in horizontal direction,
$R=v_{x}t$

$⟹v_x=\frac{R}{t}$

Hence only horizontal distance traveled needs to be known.